Implement Windows GPO support for "dlpref" in component updater.

chrome/installer/util/google_update_settings.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_SETTINGS_H_
 #define CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_SETTINGS_H_
 
 #include <stddef.h>
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 #include "base/version.h"
 #include "build/build_config.h"
 #include "chrome/installer/util/util_constants.h"
 #include "components/metrics/client_info.h"
 
 class AppRegistrationData;
 class BrowserDistribution;
 
 namespace installer {
 class ChannelInfo;
 class InstallationState;
 }
 
-// This class provides accessors to the Google Update 'ClientState' information
-// that recorded when the user downloads the chrome installer. It is
-// google_update.exe responsibility to write the initial values.
+// This class provides accessors to the Google Update group policies and
+// 'ClientState' information. The group policies are set using specific
+// administrative templates. The 'ClientState' information is recorded when the
+// user downloads the Chrome installer. It is google_update.exe responsibility
+// to write the initial values.
 class GoogleUpdateSettings {
  public:
   // Update policy constants defined by Google Update; do not change these.
   enum UpdatePolicy {
     UPDATES_DISABLED    = 0,
     AUTOMATIC_UPDATES   = 1,
     MANUAL_UPDATES_ONLY = 2,
     AUTO_UPDATES_ONLY   = 3,
     UPDATE_POLICIES_COUNT
   };
 
   static const wchar_t kPoliciesKey[];
   static const wchar_t kUpdatePolicyValue[];
   static const wchar_t kUpdateOverrideValuePrefix[];
   static const wchar_t kCheckPeriodOverrideMinutes[];
+  static const wchar_t kDownloadPreferencePolicyValue[];
   static const int kCheckPeriodOverrideMinutesDefault;
   static const int kCheckPeriodOverrideMinutesMax;
   static const GoogleUpdateSettings::UpdatePolicy kDefaultUpdatePolicy;
 
   // Defines product data that is tracked/used by Google Update.
   struct ProductData {
     // The currently installed version.
     std::string version;
     // The time that Google Update last updated this product.  (This means
     // either running an updater successfully, or doing an update check that
@@ skipping 202 matching lines @@
   // settings that would block updates from occurring. This is a superset of the
   // things checked by GetAppUpdatePolicy() as GetAppUpdatePolicy() does not
   // check Omaha's AutoUpdateCheckPeriodMinutes setting which will be reset by
   // this method. Will need to be called from an elevated process since those
   // settings live in HKLM. Returns true if there is a reasonable belief that
   // updates are not disabled by policy when this method returns, false
   // otherwise. Note that for Chromium builds, this returns true since Chromium
   // is assumed not to autoupdate.
   static bool ReenableAutoupdates();
 
+  // Returns a string if the corresponding Google Update group policy is set.
+  // Returns an empty string if no policy or an invalid policy is set.
+  // A valid policy for DownloadPreference is a string that matches the
+  // following regex:  `[a-zA-z]{0-32}`.

[gab, 2016/01/26 03:44:55]

So a policy of "abc12345" means something? Or are the meaningful values that
should be documented?

[Sorin Jianu, 2016/01/26 18:09:48]

Done.

+  static base::string16 GetDownloadPreference();
+
   // Records UMA stats about Chrome's update policy.
   static void RecordChromeUpdatePolicyHistograms();
 
   // Returns Google Update's uninstall command line, or an empty string if none
   // is found.
   static base::string16 GetUninstallCommandLine(bool system_install);
 
   // Returns the version of Google Update that is installed.
   static Version GetGoogleUpdateVersion(bool system_install);
 
@@ skipping 38 matching lines @@
   // this will do nothing to |experiment_labels|. This will return true if the
   // label did not exist, or was successfully read.
   static bool ReadExperimentLabels(bool system_install,
                                    base::string16* experiment_labels);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(GoogleUpdateSettings);
 };
 
 #endif  // CHROME_INSTALLER_UTIL_GOOGLE_UPDATE_SETTINGS_H_